The invention lies in the semiconductor technology field. More specifically, the invention relates to a process for the production of an integrated electrical circuit, in which one or more dielectric layers and one or more structured semiconductor layers as well as at least one metal plane are applied on a substrate. A monomolecular film, made up of molecules which contain at least one anchoring group, is applied as a passivation layer to the metal plane by wetting the metal plane with a solution. Metal wires are connected to the metal plane.
It is known in the art that integrated electrical circuits, which contain a metal plane, can be protected against corrosion and mechanical damage by providing the metal plane with a passivation layer.
Dielectrics (e.g. silicon nitride: Si3N4) and metal passivations (e.g. titanium, tantalum, aluminum, palladium) have to date been used as diffusion and oxidation barriers.
In order to buffer against mechanical stresses, it has been found effective to provide these passivation layers with an additional organic layer, in particular a polymer layer. The thickness of the polymer layer is at least one micron (1 xcexcm). Other organic protective layers also have a defined minimum thickness of preferably more than 200 nm.
The prior art passivation layers are used in the large-scale fabrication of integrated circuits. In prolonged operation or under high operating temperatures, however, instabilities occur which may lead to a rupture of the passivation layer. A further disadvantage of these passivation layers is the impediment caused by them when making contact with the metal plane using connection wires. It is hence necessary, before making contact, to apply a mask (by depositing resist, exposing and developing), and subsequently to treat the contact locations using anisotropic metal etching.
Japanese patent application JP-A-6041183 discloses a metal surface of a biosensor. A surface of the biosensor is covered with a monomolecular layer.
Such monomolecular layers are used as passivation layers for integrated semiconductor circuits. U.S. Pat. No. 5,264,731 discloses an integrated semiconductor circuit whose surface is first covered with a monomolecular passivation layer and then enclosed with a synthetic resin.
The object of the invention is to provide a process for the production of an integrated electrical circuit which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind, and in which, on the one hand, the passivation layer is produced in the simplest and most cost-effective way and, on the other hand, the passivation layer does not impede the connection of metal wires to the metal plane. It is a further object to render it possible for the application of the passivation layer to be integrated in the process sequence for the production of the integrated electrical circuit.
With the above and other objects in view there is provided, in accordance with the invention, a method of producing an integrated electrical circuit, which comprises:
forming one or more dielectric layers, one or more structured semiconductor layers, and at least one metal plane on a substrate;
wetting the metal plane with a solution for applying a passivation layer on the metal in the form of a monomolecular film made up of molecules containing an anchoring group; and
subsequently connecting a metal wire to the metal plane with a pressure sufficient to pierce the monomolecular film.
In other words, the passivation layer is applied before the metal wires are connected to the metal plane, and the metal wires are connected to the metal plane using a pressure which is sufficient to pierce the monomolecular film.
In accordance with an added feature of the invention, the metal plane is formed of copper, silver, or gold.
In accordance with another feature of the invention, the anchoring group of the molecules of the monomolecular film is a thiol. In a preferred embodiment, the molecules of the monomolecular film are alkanethiol molecules.
In accordance with an additional feature of the invention, the anchoring group of the molecules of the monomolecular film is a sulfide or a disulfide.
With the above and other objects in view there is also provided, in accordance with an alternative feature of the invention, a method of producing an integrated electrical circuit, which comprises:
forming one or more dielectric layers, one or more structured semiconductor layers, and at least one metal plane on a substrate;
wetting the metal plane with a solution for applying thereon a passivation layer in the form of a monomolecular film made up of molecules containing an anchoring group; and
subsequently connecting a metal wire to the metal plane by performing the following steps:
energizing the monomolecular film at locations defined for connection to the metal wires in a controlled manner using electromagnetic radiation with an energy great enough for a bonding of the molecules to the metal to be weakened at the locations; and
connecting the metal wires to the metal plane at the locations.
In other words, the alternative mode of connecting the wires to the metal layer includes the following process steps:
energy is delivered to the monomolecular film at the locations intended for connection to the metal wires in a controlled way using electromagnetic radiation. The energy is great enough for the bonding of the molecules to the metal to be weakened at these locations; and
the metal wires are connected to the metal plane at these xe2x80x9cweakened-bondxe2x80x9d locations.
In accordance with an added feature of the invention, prior to connecting the metal wires to the metal plane, a solution is applied that has a solvent power sufficient to dissolve the molecules whose bonding to the metal has been weakened in the energizing step.
In accordance with again an added feature of the invention, the film is washed with high-purity deionized water and subsequently dried with nitrogen.
In accordance with again an additional feature of the invention, the film at the specified locations is radiated with UV light.
In accordance with an alternative feature of the invention, the energizing step comprises exposing with an extra-high-pressure mercury lamp.
In accordance with a concomitant feature of the invention, the energizing step comprises exposing with a laser.
In once more summarizing the invention, a film is provided in direct contact with the surface of the metal to act as a passivation layer. Because the film consists of molecules whose adhesion to the metal surface is very strong, it is not possible for any further substances to be taken up. A monomolecular protective film is hence provided.
Such a protective film is distinguished in that it can be formed straightforwardly by dipping the electrical circuit in a solution. It is hence possible to provide more than 100 integrated electrical circuits with the passivation layer in one solvent simultaneously.
Further layers, for example an additional protective film, may be applied to the monomolecular film, although, just the monomolecular film itself is actually sufficient to obtain the desired properties of the passivation layer.
In contrast to the passivations known in the prior art, which have as large a passivation layer thickness as possible, the invention hence proposes that the passivation layer be formed in such a way that it has a minimal thickness and can bond in an ideal way conformally to the surface of the metal.
Such a bond between the metal surface and the film is obtained, according to a particularly advantageous embodiment, in that the monomolecular film consists of molecules which contain an anchoring group. The electrons of this anchoring group can interact with the metal surface. Relevant inter-action mechanisms include both physical adsorption processes as well as covalent and ionic forces.
The effect of the exothermic interaction of the anchoring group with the metal surface is that the molecules contained in solution utilize each binding site on the metal surface. A precondition for this is that the molecules need to be mobile on the surface, in order to offer further binding sites by coalescence. The surface mobility leads to the formation of highly ordered crystalline monolayers.
The molecules consist of an anchoring group, which interacts with the metal surface. This is followed by a nonpolar organic chain which may have both a linear and a branched structure. This organic chain can be substituted in various ways, that is to say the water solubility of the molecule can be increased in a controlled way by the insertion of substituents such as amides or oxygen. Such a molecule suitable for the chemisorption process may further have an end group which not only determines the surface function of the film, but also influences the ordering state, that is to say the molecular structure of the layer.
The organic chains interact with one another. A possible explanation of the intermolecular interaction could be provided by van der Waals forces. The end group points outward. The end group determines the composition of the outward-facing surface of the monomolecular film which is essential for the properties of the passivation layer.
Further molecules may be taken up on the end group, so that a further layer, which imparts additional properties to the passivation layer, can be formed on the monomolecular film.
Because the anchoring groups enter into highly exothermic bonding with the metal surface, and the individual molecules simultaneously interact strongly with one another, the application of the passivation layer leads to displacement of impurities adhering to the metal surface.
The metals may be metals customarily used in the semiconductor industry, in particular copper, gold and silver. Since the passivation according to the invention is based on an interfacial effect, the metal layer may be as thin as desired.
It is hence also possible for metal layers present inside the integrated electrical circuit to be provided with a passivation layer according to the invention. The passivation layer may particularly advantageously be applied by wetting the metal plane with a solution made up of a solvent and molecules dissolved therein, the dissolved molecules respectively containing at least one anchoring group. This leads to the formation of a monomolecular film on the metal plane.
Through the application of a solution in which the concentration of the molecules in the solvent is at least 0.5 mM, the formation of a complete layer is achieved after as little as a minute.
All the molecules mentioned above are suitable for ensuring the function of diffusion and oxidation barriers as well as good connectability of metal wires to the metal surface.
It is even possible to apply the passivation layer in such a way as to avoid creating environmentally unfriendly waste. This can be done by dissolving water-soluble molecules in water and applying this solution. Molecules with a thiol group have been found to be particularly suitable water-soluble molecules.
The integrated electrical circuits according to the invention can be connected to metal wires in a simple way. This is done in a particularly simple and, at the same time, expedient way by bonding the metal wires to the metal plane, through the film, using a pressure which is sufficient to pierce the monomolecular film.
The process of connection between the metal wires and the metal plane is advantageously integrated in the process sequence for the production of the integrated electrical circuit by delivering energy in a controlled way to the monomolecular film at the locations intended for connection to the metal wires using electromagnetic radiationxe2x80x94preferably using UV light, the energy of the electromagnetic radiation being great enough for the bonding of the molecules to the metal to be weakened at these locations. If appropriate, a solution is then applied whose solvent power is sufficient to dissolve the molecules whose bonding to the metal has been weakened. The metal wires are subsequently connected to the metal plane at these locations.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an integrated electrical circuit with passivation layer, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.